The exploration for the next generation of anode materials in the lithium-ion batteries is a vital subject in the past few years due to the huge demand of high capacity batteries. Silicon (Si) stands out as a promising anode material due to its high theoretical specific capacity (4200 mAh/g), enviroment friendliness and low costs. However, Si nanoparticles (NPs) experience severe volume changes up to 300 % during the lithiation/delithiation process, which leads to dramatic particle degradation and thus capacity loss. Novel polymeric binders with enhanced mechanical properties have been identified as one effective approach to alleviate this issue, and some examples include carboxymethyl cellulose (CMC), alginate, and poly(acrylic acid) (PAA), etc. By using those binders, cell performance has been greatly improved as compared to the conventional polyvinylidene fluoride (PVDF) binder. Among those candidates, PAA outperforms others possibly due to its superior mechanical properties. In this report we have attempted to investigate the lithiation effect of the PAA binders. Lithiating PAA binders could benefit the electrode laminate processing as well as cycling performance. A commercially available PAA sample with a characterized M_n of 147 kDa was used in this study. By titrating with LiOH solution, we controlled the pH of 10 wt% PAA solutions as well as the lithiation ratio (Table 1). Those binder solutions were used to fabricate silicon/ graphite composite electrodes that composed of 10 % PAA, 73 % Hitachi MagE, 15 % Si NPs (NanoAmour, 70-130 nm), and 2 % Timcal C45. Half-cell cycling results (Figure 1) indicated that different lithiation of PAA binders has dramatic impact on their corresponding cycling performance. Lower lithiation tends to afford higher initial specific capacities and better capacity retentions. Actually, the best performer is PAA binder with no lithiation at all. This result is a little contradicting to previous study but we reason that our lithiation agent, LiOH, may have side reasons with silicon particles, as evidenced by the dramatic decrease of the silicon capacity. Full cell cycling as well as further characterization of electrode surface is ongoing.

Table 1. The calculated mol% of LiOH (to AA monomer) and the resulting pH values of the final PAA solutions.

LiOH %	0	25	50	75	85	90	91	92.5	95	100
pH	2.08	4.22	4.84	5.49	5.97	6.97	10.03	11.96	12.28	12.59

Figure 1. Specific discharge capacity and Coulombic efficiency of PAA binders with different pH values.